CORRESPONDENCE: LETTER TO THE EDITOR
Standard Deviation of Sequential Five-Minute R-R Interval Means (SDANN) Is a Prognostic Marker, but Not Necessarily an Autonomic Marker
Satish R. Raj, MD, MSCI,
Daniel E. Roach, PhD,
Mary Lou Koshman, RN and
Robert S. Sheldon, MD, PhD*
* Libin Cardiovascular Institute of Canada, 3330 Hospital Drive NW, Calgary, Alberta, T2N 4N1 Canada (Email: sheldon{at}ucalgary.ca).
The recent study by Fantoni et al. (1) provides strong data that standard deviation of sequential 5-minute R-R interval means (SDANN, a long-term measure of heart rate variability [HRV]) is an important clinical tool. The researchers have convincingly shown that 1) successful cardiac resynchronization therapy (CRT) improved SDANN and 2) that an early improvement in SDANN predicted a favorable long-term outcome.
The investigators interpret this increase in SDANN as reflecting changes in autonomic tone, specifically modifications of the sympathetic nervous system and parasympathetic nervous system interactions in the heart. Although we agree that short-term measures of HRV such as high-frequency (0.15 to 0.4 Hz) and low-frequency (0.04 to 0.15 Hz) variability have been shown to be modulated by the autonomic nervous system, there are no data showing that SDANN is a reflection of the autonomic nervous system.
In contrast, we have shown that SDANN is heavily influenced by physical activity. In an earlier study, the largest contributions to the SDANN came around the transitions going into and waking from sleep (2). We have also shown in both patients with heart failure and in healthy subjects that SDANN significantly increased by changing the activity level from periods of enforced rest to periods of scripted activity (3). Finally, we could generate similar SDANN values by dual-chamber pacing whether driven by sinus node activity or by a mechanical activity sensor (4). Taken together, these findings indicate the major role of activity in inducing SDANN.
Fantoni et al. found that the increases in SDANN were parallel to improvements in functional capacity, and Adamson et al. (5) reported that a decline in physical activity corresponded with a decrease in SDANN prior to a clinical deterioration.
We propose that patients with successful CRT experience hemodynamic improvements, an improvement in functional capacity, and an increase in physical activity with the resultant modulation of heart rate, which is reflected by an increase in SDANN. Finally, none of this diminishes the importance of SDANN, but does suggest that its important role may not involve the autonomic nervous system.
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Footnotes
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Please note: Dr. Raj was supported by grant K23-RR020783 from the National Institutes of Health. This work was supported by grant GR13914 from the Canadian Institutes of Health Research (formerly the Medical Research Council of Canada), Ottawa. Dr. Roach was a Postdoctoral Fellow of the Heart and Stroke Foundation of Canada, Ottawa.
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References
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- Fantoni C, Raffa S, Regoli F, et al. Cardiac resynchronization therapy improves heart rate profile and heart rate variability of patients with moderate to severe heart failure J Am Coll Cardiol 2005;46:1875-1882.[Abstract/Free Full Text]
- Roach D, Sheldon A, Wilson W, Sheldon R. Temporally localized contributions to measures of large-scale heart rate variability Am J Physiol 1998;274(5 Pt 2):H1465-H1471.
- Roach D, Wilson W, Ritchie D, Sheldon R. Dissection of long-range heart rate variability: controlled induction of prognostic measures by activity in the laboratory J Am Coll Cardiol 2004;43:2271-2277.[Abstract/Free Full Text]
- Raj SR, Roach DE, Koshman ML, Sheldon RS. Activity-responsive pacing produces long-term heart rate variability J Cardiovasc Electrophysiol 2004;15:179-183.[CrossRef][ISI][Medline]
- Adamson PB, Smith AL, Abraham WT, et al. Continuous autonomic assessment in patients with symptomatic heart failure: prognostic value of heart rate variability measured by an implanted cardiac resynchronization device Circulation 2004;110:2389-2394.[Abstract/Free Full Text]
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